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Superconductivity is a phenomenon in which an electric circuit loses its resistance and becomes extremely efficient under certain conditions. There are different ways in which this can happen, which were thought to be incompatible. For the first time, researchers have discovered a bridge between two of these methods to achieve superconductivity. This new knowledge could lead to a more general understanding of the phenomenon, and one day to applications.

There are three well-known states of matter: solid, liquid and gas. There is a fourth state of matter called plasma, which is like a gas that got so hot all its constituent atoms came apart, leaving behind a super-hot mess of subatomic particles. But there is a fifth state of matter at the complete opposite end of the thermometer known as a Bose-Einstein condensate (BEC).

"A BEC is a unique state of matter as it is not made from particles, but rather waves," said Associate Professor Kozo Okazaki from the Institute for Solid State Physics at the University of Tokyo. "As they cool down to near absolute zero, the atoms of certain materials become smeared out over space. This smearing increases until the atoms—now more like waves than particles—overlap, becoming indistinguishable from one another. The resulting matter behaves like it's one single entity with new properties the preceding solid, liquid or gas states lacked, such as superconduction. Until recently superconducting BECs were purely theoretical, but we have now demonstrated this in the lab with a novel material based on iron and selenium (a nonmetallic element)."

This is the first time a BEC has been experimentally verified to work as a superconductor; however, other manifestations of matter, or regimes, can also give rise to superconduction. The Bardeen-Cooper-Shrieffer (BCS) regime is an arrangement of matter such that when cooled to near absolute zero, the constituent atoms slow down and line up, which allows electrons to pass through more easily. This effectively brings the electrical resistance of such materials to zero. Both BCS and BEC require freezing-cold conditions and both involve atoms slowing down. But these regimes are otherwise quite different. For a long time, researchers have believed that a more general understanding of superconduction could be reached if these regimes could be found to overlap in some way.

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